1. Field of the Invention
The present invention provides a method for the production sinter dolomite, whereby primarily carbonate raw materials are ground, pressed into a predetermined shape, such as briquettes, an then sintered.
2. Description of the Prior Art
Sintered dolomite may serve as the refractory basic material for the production of basic refractory bricks. For the production of high grade refractory bricks, the sinter has, as primary requisites, a low amount of contamination from foreign oxides, for example, which is less than 3.5%, and a high density, for example, which is a raw density which is greater than 3.15 g/cm.sup.3. Known procedures, such as a procedure according to Austrian Patent No 66278, call for the burning of magnesite which has been pre-deacidified in a rotary kiln. This procedure, however, produces a very uneven sinter, due to the degree of burning and, therefore, cannot be used for the sintering of dolomite which meets the above-mentioned requirements.
If one starts with raw dolomite gravel with a grain size between approximately 6 mm and 30 mm and heats it at a temperature which is greater than 2000.degree. C., a raw density of the sinter dolomite of approximately 3.20 g/cm.sup.3, with a contamination by foreign oxides of less than 3.5%, can be achieved Raw materials, which can be sintered only with difficulty, will be deacidified only with a first burn such as that described in German Patent No. 31 18 481. After the first passage through the kiln, the raw material is then graded and compacted and is then sintered in a second passage through the kiln. The expenditure in energy is somewhat large because of the required high temperatures and the two stage burning. During the preparation of raw dolomite gravel, there are substantial amounts of raw dolomite sand with a grain size of less than 6 mm. It is not possible to compact the necessarily produced grains in a direct manner.
A further lowering of the lower size limit for the gravel is not permitted because of the otherwise increasing aerodynamic resistance of the fill at the Lepol grate which is, normally, attached to the rotary kiln and ahead of the entry to the kiln as recited, for example, in German Patent Publication for Opposition Purposes No. 16 46 918.
Furthermore, during the dust removal from the rotary kiln, a fine-grained filter dust is encountered which contains primarily oxides and has an upper limit of the grain spectrum of about 0.5 mm. This oxide filter dust can, however, be turned into briquettes and can be sintered, but the obtainable raw density of the sinter dolomite briquettes is too low since it is at a level of less than 3.10 g/cm.sup.3. These residues, from the typical production methods of sinter dolomite from raw dolomite gravel, now have to be used in some other manner or else have to be disposed of.
German Laid Open Application No. 32 09 836 describes how to provide ground raw dolomite with additives and how to make briquettes which are then deacidified and sintered in a shaft kiln It is possible to add additives in a planned fashion and to receive valuable sinter dolomite in one single passage through the shaft or pit furnace. This procedure is limited to being performed in a shaft or pit furnace because of the brittle characteristics of the briquette. The briquettes have, at the temperature level at which a deacidification takes place, a very high porosity which can be up to 60%. The rotary kiln, by comparison to the shaft or pit furnace, has a higher mechanical or abrasive wear and tear. Briquettes could not be made from, primarily, carbonate raw material because they would become destroyed. Even if one, as suggested in German Laid Open Patent Application No. 25 53 001, uses finely ground raw materials prepared by flotation and increases the press pressure for the formation of the mold, it is not possible to obtain a sinter raw density of greater than 3.2 g/cm.sup.3 with dolomite. Even the procedure for the production of briquette sinter, according to German Patent No. 31 18 481, cannot succeed without the addition of additives to the raw dolomite.